Speed-regulating system



Oct. 9, 1962 J. A. HERR 3,

SPEED-REGULATING SYSTEM Filed Nov. 5, 1960 IN VEN TOR. JOHN A. HERR WITNESS TORNEY United States Patent Manufacturing Company, Elizabeth, N .J., a corporation of New Jersey Filed Nov. 3, 1960, Ser. No. 67,063 2 Claims. (Cl. 318-246) This invention relates to speed-regulating systems for small electric motors having series-connected armature and field windings fed from an AC. supply voltage source,

The system of the present invention may be considered an improvement over that shown and described in the United States Patent No. 2,939,064 (assigned to the same assignee as the present invention).

In the system of the prior invention a solid state controlled rectifier controls the current flow to the motor windings. The gate voltage for the rectifier is produced by balancing the speed-responsive armature voltage against an adjustable preselected reference voltage obtained from the source voltage by a resistance voltage divider using a potentiometer with a sliding contact. It has been found that the sliding contact is not desirable in the gate circuit as it may produce intermittent a plication and/or removal of the gate voltage, which has a deleterious efiect on the rectifier unit itself.

The present invention eliminates this diificulty by using a variable inductance element in place of the resistance potentiometer. With this construction, the gating circuit is always closed conductively, the variations in the reference voltage being smoothly accomplished by varying the reluctance of the magnetic circuit of the inductauce winding.

It is therefore an object of this invention to provide a speed-regulating system for an electric motor using a gate-controlled solid state rectifier to control the current to the motor and in which the gate circuit for the rectifier remains closed conductively at all times.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawing of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby, will be readily understood by those skilled in the art.

The sole FIGURE of the drawing is a schematic wiring diagram of a system embodying the invention.

Referring to the figure, it will be seen that the circuit shown is the same as that shown and described in the United States Patent No. 2,939,064 except that, in place of the potentiometer 14 of the patent, there is substituted a variable inductance controller having a coil 11 connected permanently in series across the line L-L with a fixed resistor 12. Variation in the inductance of the coil 11 is controlled by varying the reluctance of the magnetic circuit through the coil, as by movement of a magnetic plunger 13 into and out of the magnetic circuit threading the coil. This controls the impedance voltage drop across the coil 11 to establish a variable reference voltage for the gate.

It is to be noted that, with this construction, there is no rubbing frictional contact such as formerly was the case with the slider of the potentiometer. That is to say, the gate circuit of the present invention remains conductively closed at all times, thus removing the possibility of adverse transient voltages on the gate and greatly increasing the reliability of operation and life of the rectifier itself.

A resistor 14 may be placed in shunt with the coil 11 to establish a top limit to the impedance of the unit. A zero impedance may be obtained by a switch 15 which shorts out the coil in the maximum reluctance or off position of the controller as shown. The controller 10 is normally biased to the off position by a compression spring 16.

Operation In the position shown, the switch 15 shorts out the shunt arrangement of coil 11 and resistor 14. In this condition no reference voltage can be supplied to fire the solid state rectifier 17 and thus no current can flow in the field winding 18 or armature winding 19 and the motor is at a standstill.

When the operator pushes down on the plunger 13, the switch 15 opens and allows a reference voltage to appear across the resistor 14 of a value determined by the resistance of the resistor 14 and the reactance of the coil 11, which latter depends on the position of the plunger 13. The rectifier 17 will fire to supply current to the motor windings 18 and 19 and the motor will accelerate to a speed at which the back voltage of the armature winding balances the reference voltage to reduce the gate voltage to a value that cuts off the rectifier. The motor then slows down until the reference voltage overcomes the back armature voltage to again fire the rectifier 17 and the process repeats. It will be seen that the motor thus assumes an average speed set by the reference voltage as determined by the position of the plunger 13. At any instant the motor speed may be slightly above or below this average depending on whether the rectifier 17 is conducting or non-conducting.

As the plunger 13 is pushed in further, the reluctance of the magnetic circuit linking the coil 11 is reduced thus increasing the reactance of the coil 11 which increases the reference voltage and the average speed of the motor as desired.

Having thus set forth the nature of the invention, what I claim herein is:

l. A speed regulating system for an electric motor having series-connected field and armature windings fed from an A.C. supply voltage comprising a solid state controlled rectifier having an anode-cathode circuit in series with said field and armature windings, a gatecathode control circuit, a signal channel including said motor armature winding for transmitting to said gate cathode control circuit the back of said motor as negative bias therefore, adjustable inductance means for producing a selected reference signal, and means connecting said reference signal in series opposition to said motor back whereby the algebraic sum of the back E.M.F. and the reference signal is supplied to the gatecathode control circuit.

2. In an electrical control system, the combination of an electric motor adapted to be connected to an AC. source and having series-connected armature and field windings, with asolid state controlled rectifier having an anode-cathode circuit connected in series with said armature and field windings and having a gate-cathode control circuit, a signal channel including said armature winding for transmitting to said gate-cathode control circuit the back of said motor as negative bias therefore, means connected to said A.C. source including an inductance coil with manually-actuated means for varying the reluctance of the magnetic circuit threading said coil to produce a selected reference signal, and 10 References Cited in the file of this patent UNITED STATES PATENTS Momberg et a1 May 31, 1960 Momberg et a1 Apr. 25, 1961 

